The present invention relates to the automotive vehicle arts. It finds particular application in conjunction with off-loading cargo from tanker trucks or tractor trailer combination vehicles and will be described with particular reference thereto. It will be appreciated, however, that the present invention is also applicable to other fields and is not limited to the aforementioned application.
Typically, when a tanker truck is ready to off-load a bulk product, a driver applies a parking brake, and any other safety measures to keep the truck or tractor trailer stationary before off-loading. With many products, the off-load process is pressurized to assist flow of product from the tank. This quite often is a lengthy process, sometimes taking in excess of five hours.
Tanker trucks are equipped with pneumatic hardware that in normal operation is used to provide pressure for various air operated devices such as brakes. When the driver activates the pump-off mode, the pneumatic system supplies pressure to the truck bulk tank or trailer bulk tank.
To avoid complications, compressed air is dried and often filtered before it is used in pneumatic applications. Typically, the compressor is run at a constant pressure, e.g., on the order of about 85 psi or about 590 kPa, during pump-off. This pressure is required so that there is sufficient back pressure to fill purge volumes of the dryers for regenerating the desiccant that adsorbs moisture from the compressed air system. As is known, the purge volumes included in commercially available air dryers flush moisture from the dryer after it has been operating for a predetermined time. During a charge cycle, high pressure is used for adsorption and moisture is removed from the compressed air and retained by the desiccant. During the desorption process, the desiccant is regenerated at low pressure by using high pressure and expanding through an orifice. So, in a conventional system, a pressure protection valve is provided and the rest of the system backs up or builds to the level of this valve. The volume of the stored air is then expanded so that if the pressure protection valve is eliminated, then the system can operate at less than 20 psi. This is an inefficient process given that the compressor is running at an elevated level such as a constant 590 kPa when a reduced pressure, typically on the order of 20 psi or 135-175 kPa, is adequate to off-load the tank. In other words, the compressor is working harder than it needs to thereby shortening its overall life. Additionally, the compressor flow is higher when operating at lower pressures.
Pump-off systems commonly employ a pressure regulation valve. Typical tankers handle 20 psi or 135-175 kPa during the off-load process. Since the compressor is running at higher pressure to enable the dryers to be properly purged as noted above, this valve is included to reduce the pressure (e.g. to 135-175 kPa) for the pump off process.
The present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others.
In accordance with one aspect of the present invention, a system for providing pressure to assist a cargo off-load is provided.
A preferred embodiment of the invention includes an air compressor supplying pressurized air to the associated bulk product off-load. A dryer removes moisture from the air supplied by the compressor. A brake system service reservoir(s) provides compressed air for purging the dryer of moisture, thereby allowing the compressor to operate at a reduced pressure level and increased efficiency.
In accordance with another aspect of the present invention, a method of off-loading product from a tanker truck is provided. The method includes the steps of supplying pressurized, dry air to a product tank and purging the dryer with air from a service reservoir.
In accordance with another aspect of the present invention, a tanker truck has a cargo hold for retaining a flowable bulk product and a pressurized off-load assist system. The off-load assist system alternately compresses air at high and low pressures, the high pressure being used to pressurize at least one service reservoir, and the low pressure being used to pressurize an off-load.
One advantage of the present invention resides in more efficient compressor operation.
Another advantage relates to longer compressor life.
Another advantage is realized by faster bulk product off-load times.
Still another advantage is the improved utilization of existing hardware.
Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.